Method for introducing coal into a blast furnace



July 27, 1965 J. c. AGARWAL METHOD FOR INTRODUCING COAL INTO A BLASTFURNACE Filed 061:. 12. 1961 D E S S m A M i FLOW OIVTROL L 5!? TUYERESCOLD BLAST MAIN INVENTOR. JAGD/SH C. AGARWAL M/ Attorney United StatesPatent 3,197,304 METHOD FOR WIRODUCING COAL INTO A BLAST FURNACE.Iagdish C. Agarwal, Penn Hills Township, Allegheny County, Pa, assignorto United States Steel Corporation, a corporation of New Jersey FiledOct. 12, 1961, Ser. No. 144,605 2 Claims. (Q1. 75-42) This inventionrelates to an improved method and apparatus for handling pulverized coalintroduced to a blast furnace through the tuyeres.

In conventional blast furnace operation, iron ore, metallurgical cokeand limestone flux are charged to the top of the furnace, while a hotair blast is blown through the tuyeres. Since proper grades of coke arescarce and costly, every effort is made to use smaller proportions ofcoke. It is known that the coke consumption can be lowered byintroducing fuel with the blast at the tuyeres. Such fuel may be eithergaseous, liquid or pulverized solids, and it oxidizes in the furnace tofurnish part of the necessary heat. Pulverized coal presents handlingproblems when used for this purpose. It is necessary to dry the coal sothat freezing of condensed moisture in cold weather does not impede itsfiow. Furthermore the size range of the coal particles must becontrolled for proper regulation of the injection rate.

An object of my invention is to provide an improved method and apparatusfor handling pulverized coal in which the coal is sized, dried andinjected in regulated quantities through the tuyeres of a blast furnaceall in one continuous operation.

A further object is to provide a method and apparatus for handlingpulverized coal in which coal particles are dried in a bed fiuidized byair taken from a cold blast main and heated to a suitable dryingtemperature and subsequently injected along with the air blast to thefurnace.

In the drawing:

The single figure is a diagrammatic showing of a coal handling apparatusconstructed in accordance with my invention.

My apparatus includes a storage bin containing a supply of crushed coal,a pulverizer 12, conveyors 13 for feeding coal from the bin to thepulverizer, and a screen 14 or equivalent for separating oversizeparticles from the pulverized product. Usually I screen at 4; inch orinch, and I return oversize particles to the pulverizer for furthergrinding. A conveyor carries coal particles which pass through thescreen to the mouth of a container 16. Two outlet conduits 17 and 17aextend from the bottom of container 16 to alternative hoppers 18 and18a. I equip these conduits with respective valves 19 and 19a, whichseal the upper ends of the hoppers air-tight when closed. I connectcompressed air lines 29 and 20a, which contain valves 21 and 21a, to therespective hoppers 18 and 18a. I alternately open one valve 17 or 17aand close the other and thus fill each hopper 18 and 18a in turn withpulverized coal from container 16. I close valve 21 or 21a which leadsto the open hopper and open the other to pressurize the closed hopper.

My apparatus includes a fluidized bed dryer 22 and respective screwconveyors 23 and 23a and downcomers 2d and 24a for continuously feedingpulverized coal from the closed hopper 18 or 18a to said dryer. Icontinuously withdraw a controlled portion of the compressed air carriedby a cold blast main 25 through a line 26 which contains a flowcontroller 27. Line 26 leads to a compressor 23, thence to adirect-fired heat exchanger 29, and finally to the dryer 22. I compressthe air to a pressure of about 50 to 60 p.s.i.g., which is about 20 to30 pounds higher ice than the pressure in the tuyere zone of a blastfurnace. Pressure in the closed hopper 18 or 18a balances pressure inthe dryer, while the screw conveyors 23 and 2311 have conventional locksto prevent loss of pressure through the open hopper. I heat the air to atemperature of about 1400 to 1900 F. to maintain a temperature of 220 to350 F. in the dryer. I control this temperature with a temperaturesensing element 30 connected to the dryer and a flowproportioning valve31 in the fuel line to the heat exchanger operatively connected to saidsensing element. Alternatively I can adjust valve 31 manually inaccordance with the temperature readings. As another alternative, I canuse direct means for preheating the air, such as by burning fuel in theair stream, or I can use other compatible gas than air.

Dryer 22 has a constriction plate 32 which supports a bed of coalparticles B. Air from line 26 enters the bottom of the dryer below theconstriction plate and passes upwardly therethrough to fluidize the bed.The pressure drop between the dryer and the tuyere zone of the furnacecontinuously forces air and entrained coal particles from the bedthrough a series of downcomers 33 which lead to the respective tuyeresof the blast furnace (not shown). I position these downcomerssymmetrically around the dryer to ensure that each receivesapproximately an equal quantity of coal. All the air withdrawn from themain passes through the dryer and ultimately reaches the blast furnace,except for minor leakage. While I prefer that each downcomer lead to asingle tuyere, alternatively each can feed coal to two or more tuyeres,or the same dryer can be used for more than one blast furnace. I controlthe total quantity of coal feeding from the dryer by regulating thespeed of the screw conveyors 23 and 23a and by regulating the compressor28.

As a specific example to demonstrate how my invention may be practiced,I operated a blast furnace having a 23- foot hearth diameter with atotal blast of 65,000 s.c.f./ minute. I bypassed approximately 5 percentof this blast (3,250 s.c.f./min.) from the cold blast main and heatedthe remainder to the usual temperature of about 1650" F. I compressedthe bypassed air from 35 p.s.i.g. to 50 p.s.i.g. and heated it to 1900F. in a direct-fired heat exchanger. I fed coal to the dryer at a rateof 20 tons an hour, while maintaining a fluidization velocity of 1.5feet per second and a bed temperature of 300 F. From the bed of thedryer, I fed 20 tons of coal an hour and 3250 sci/minute of air throughsixteen downcomers connected to a like number of tuyeres of a furnace.The coal flowed freely and distributed itself uniformly to thediflferent tuyeres where it oxidized, as known in the art. I was able toreplace 1.15 pounds of coke for each pound of coal injected at thetuyeres.

From the foregoing description it is seen that my invention affords asimple effective method of handling and sizing pulverized coal injectedinto the tuyeres of a blast furnace. I dry and inject the coal as partof the blast all in one continuous operation. The individual items whichform my apparatus are conventional per se; hence I have not shown nordescribed them in detail.

While I have shown and described only a single embodiment of myinvention, it is apparent that modifications may arise. Therefore, I donot wish to be limited to the disclosure set forth but only by the scopeof the appended claims.

I claim:

1. A method of handling pulverized fuel for injection through thetuyeres of a blast furnace comprising continuously feeding fuelparticles from one of two alternative sources to a bed, fiuidizing theparticles in said bed with heated air maintained at a higher pressurethan the pressure at the tuyere zone of the furnace, thereby drying theparticles, pressurizing the source from which particles are feeding tothe bed to balance the bed pressure, entraining the fuel particles inthe fluidizing air, continuously forcing substantially all thefluidizing air and particles en-' trained therein from the bed inapproximately equal portions, and directing said portions individuallyfrom the bed to the respective tuyeres.

2. A method of handling pulverized fuel for injection through thetuyeres of a blast furnace comprising continuously feeding fuelparticles from one of two alternative sources to a bed, fluidizing theparticles in said he with air heated to a temperature of about 1400 to1900 F. and at a pressure about 20 to 30 p.s.i. higher than the pressureat the tuyere zone of the furnace, thereby maintaining a temperature ofabout 220 to 350 F. in said bed and drying the particles, pressurizingthe source from which particles are feeding to balance the bed pressure,entraining the fuel particles in the fiuidizing air, continuouslyforcing substantially all the fluidizing air and particles entrainedtherein from the bed in approximately equal portions, and directing saidportions individually from the bed to the respective tuyeres.

References Cited by the Examiner UNITED STATES PATENTS 719,320 1/03Foster 75-42 1,535,174 4/25 McGregor 75--42 1,541,731 6/25 Muguet 75-422,420,398 5/47 Kenney 75-42 2,719,083 9/55 Pomykala 75-42 2,841,102 7/58Mashall 110-106 2,849,968 9/58 Krug 110-106 2,939,411 6/60 Priestley110-28 3,056,212 10/62 Jamison 34-10 DAVID L. RECK, Primary Examiner.

RAY K. WINDHAM, WINSTON A. DOUGLAS,

Examiners.

1. A METHOD OF HANDLING PULVERIZED FUEL FOR INJECTION THROUGH THETUYERES OF A BLAST FURNACE COMPRISING CONTINUOUSLY FEEDING FUELPARTICLES FROM ONE OF TWO ALTERNATIVE SOURCES TO A BED, FLUIDIZING THEPARTICLES IN SAID BED WITH HEATED AIR MAINTAINED AT A HIGHER PRESSURETHAN THE PRESSURE AT THE TUYERE ZONE OF THE FURNACE, THEREBY DRYING THEPARTICLES, PRESSURIZING THE SOURCE FROM WHICH PARTICLES ARE FEEDING TOTHE BED TO BALANCE THE BED PRESSURE, ENTRAINING THE FUEL PARTICLES INTHE FLUIDIZING AIR, CONTINUOUSLY FORCING SUBSTANTIALLY ALL THEFLUIDIZING AIR AND PARTICLES ENTRAINED THEREIN FROM THE BED INAPPROXIMATELY EQUAL PORTIONS, AND DIRECTING SAID PORTIONS INDIVIDUALLYFROM THE BED TO THE RESPECTIVE TUYERES.